Generators of high-voltage electric pulses which last for only a short period are known. The duration of pulses delivered by some of these generators can be adjusted, but in contrast, it is not possible to modify the voltage waveform of these pulses which depends essentially on the type of generator and on the type of load circuit connected to the output terminals of the generator.
These pulse generators can be applied to cutting out portions of defined duration from laser pulses. For this purpose, the output terminals of an electric pulse generator are connected to the electrodes of an electro-optical shutter disposed on the path of a laser pulse which is to be cut, said laser pulse being delivered by a laser generator. The electric pulse generator is synchronized with the laser generator so that the electric pulse, which lasts for a very much shorter time than the laser pulse, is delivered during the time that the laser pulse is passing through the shutter. The shape of the laser pulse thus cut out depends on the rising and falling wave-fronts of the electric pulse and on the waveform of the laser pulse delivered by the laser generator.
In some applications, the cutout portion of the laser pulse is not only required to have a predetermined duration, but also a predetermined waveform; the latter requirement cannot be complied with when using presently known electric pulse generators.
It is possible to use a laser generator which generates very short pulses to generate longer laser pulses which have a predetermined waveform by disposing an optical device on the emission axis of the laser generator said device comprising successively a polarizer, a quarter-wave plate, several semi-transparent mirrors and a reflector. But this method is rather tricky in use, since it requires relatively complicated prior calculations.
The present invention aims to generate very simply an electric pulse of a predetermined shape and thus to cut out a portion of predetermined waveform from a laser pulse.